We have previously demonstrated that multiple immunizations with vector-based vaccines containing transgenes for tumor antigens and a triad of costimulatory molecules (TRICOM) enhance the expansion and functional avidity of antigen-specific memory CD8+ T cells in a mouse model. However, the effect of enhanced costimulation on human memory CD8+ T cells is still unclear. The study reported here was an in vitro investigation of the proliferation and function of carcinoembryonic antigen (CEA)-specific human memory CD8+ T cells following enhanced costimulation. Our results demonstrated that TRICOM costimulation enhanced production of multiple cytokines and expansion of CEA-specific memory CD8+ T cells. The lytic capacity of memory cytotoxic T lymphocytes (CTLs) toward CEA+ tumors was also significantly enhanced. Interleukin-2R-alpha (CD25) was upregulated dramatically following antigen-presenting cell (APC)-TRICOM stimulation, suggesting that the enhanced expansion of memory CD8+ T cells may be mediated by increased expression of IL-2R on memory T cells. The enhanced cytokine production and proliferation following TRICOM signaling was completely blocked by the combination of neutralizing antibodies against B7-1, ICAM-1, and LFA-3, the costimulatory molecules comprising TRICOM. No difference in T-cell apoptosis was observed between APC-TRICOM and APC-wild-type groups, as determined by annexin V, Bcl-2, and active caspase-3 staining. Results indicated that enhanced costimulation greatly expanded human CEA-specific CD8+ T cells and enhanced T-cell function, without inducing increased apoptosis of CEA-specific memory CD8+ T cells. Tumor-associated antigens are weakly immunogenic. Human carcinoembryonic antigen (CEA) is overexpressed on a wide range of human carcinomas and represents an attractive target for cancer immunotherapy. This project analyzes the ability of a Saccharomyces cerevisiae vector containing the transgene encoding CEA (yeast-CEA) to activate human dendritic cells (DCs) and stimulate CEA-specific T-cell responses. We demonstrate for the first time that treatment with yeast-CEA can activate human DCs, resulting in increases in surface expression of CD80, CD83, CD54, CD58, and MHC class II, and increased production by DCs of IL-12p70, TNF-alpha, IFN-gamma, IL-8, IL-2, IL-13, IL-10, and IL-1beta. We also show that human DCs treated with yeast-CEA can activate CEA-specific T-cell lines and can act as antigen-presenting cells (APCs) to generate CEA-specific T-cell lines capable of lysing CEA+ human tumor cells. Gene expression profiles of human DCs treated with yeast-CEA show increased expression of numerous genes involved in the production of chemokines and cytokines and their receptors, and genes related to antigen uptake, antigen presentation, and signal transduction.